Russia's S-300 missile system could dramatically change the stakes in the Syrian conflict if it is sent to Damascus, which Russia has signed a contract to do. RFE/RL lays out five things to know about the air-defense system.

What are the capabilities of the S-300 system?

The S-300 missile system is designed to shoot down aircraft and missiles at a range of 5-to-150 kilometers. That gives it the ability to destroy not only attackers in Syrian airspace but also any attackers inside Israel.

It can track and strike multiple targets simultaneously at altitudes ranging from 10 meters to 27,000 meters.

"The S-300 is Russia's top-of-the-range air-defense system," says Robert Hewson, the London-based editor of "IHS Jane's Air-Launched Weapons." "It is a surface-to-air missile system that's capable of shooting down any modern combat aircraft or missiles, including cruise missiles. In a way, it is the Russian equivalent to the U.S. Patriot system. And what it does for Syria is it adds a whole new level of capability on top of the existing Syrian air defenses. Syria already has a lot of Russian [surface-to-air] missiles, but the S-300 would be the most advanced."

How much would a deployed S-300 system complicate a decision by the international community to create no-fly zones in Syria?

The deployment of the S-300 system would greatly complicate any such measures in Syria.

It would similarly complicate Israel’s policy of striking targets in Syria to prevent transfers of sophisticated weapons from Damascus to the Lebanese Hizballah, Israel’s sworn enemy.

NATO used no-fly zones in 2011 to end the conflict in Libya. The zones protected civilians and allowed allied planes to destroy Libyan government units who were using force against populated areas.

A launch of the S-300 air-defense system

When might Russia deliver the S-300 system to Syria?

That is the big unknown. Moscow and Damascus signed the deal roughly a year before civil unrest against the Syrian regime erupted in March 2011. A firm delivery date has yet to be set.

Syrian President Bashar al-Assad said on May 30 that the systems were on the way but that report was contradicted by Russian defense analysts speaking anonymously to Russian media.

One defense source told Russia's "Kommersant" daily that the weapons contract requires Moscow to deliver the S-300 system by spring 2014.

Russian officials have refused to speak publicly about a time frame. Deputy Foreign Minister Sergei Ryabkov told reporters this week, "I can only say that we won't cancel the contracts."

Are there reasons to suspect Russia is bluffing when it says it will send the missiles?

In truth, delivering the missiles could bring huge risks for Moscow. That is because the batteries likely would have to be operated by Russian crews before Syrian teams could be completely trained in their use.

"It is standard Russian practice to send your own military advisers to go in with a new customer and help train them up," Hewson says. "And one risk in attacking [the new] S-300 -- were that to happen and if the missiles had just arrived in Syria -- is that you would hit Russian personnel that are with them."

Israel, a U.S. ally, has threatened to destroy the missiles if they are deployed. If it did and caused Russian casualties, there would be a grave risk the conflict could escalate into a superpower confrontation.

Michael Elleman, a missile expert at the International Institute for Strategic Studies' Middle East office in Bahrain, says promising to send the new missiles likely serves Moscow's purposes better than actually delivering them.

"Ultimately for Russia, I think the threat of transferring the S-300, the ambiguity as to whether it has been sent or not, probably is their best-case scenario," Elleman says. "Whereas if they do transfer it, bad things might happen and escalation is something that I don't think anyone would really like to see."

Could foreign powers find ways to circumvent the S-300 system if it were deployed?

One way to circumvent air-defense systems is to try to disrupt their operations through electronic techniques rather than attack them directly. But Elleman says it is an open question whether the S-300 could be blocked this way.

"Electronic warfare and spoofing of systems in quite common," he says, "but one must keep in mind that the S-300 is a very sophisticated piece of weaponry. And I am not convinced that the West, Israel, or Turkey could reliably neutralize the system without taking some kind of kinetic action -- in other words, going after some of the radar or some of the interceptors [with force]. So, in terms of circumventing, I think it would be very difficult and very risky."